1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to a belt unit including a belt that contacts or separates from an object and an image forming apparatus including the belt unit.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a transfer sheet such as a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member; an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a transfer sheet or is indirectly transferred from the image bearing member onto a transfer sheet via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the transfer sheet; finally, a fixing device applies heat and pressure to the transfer sheet bearing the unfixed toner image to fix the unfixed toner image on the transfer sheet, thus forming the image on the transfer sheet.
In image forming apparatuses that employ a belt as an intermediate transfer member (hereinafter referred to as an intermediate transfer belt), when transferring a toner image formed on a photoconductive drum onto the intermediate transfer belt, the intermediate transfer belt needs to contact the photoconductive drum. However, if the intermediate transfer belt remains in continuous contact with the photoconductive drum, charge remaining on the intermediate transfer belt degrades the photoconductive layer of the photoconductive drum, producing an uneven electric potential on the photoconductive drum that results in uneven images.
In a case of forming a monochrome image with a color image forming apparatus, only a photoconductive drum for the color black is used to form the monochrome image while other photoconductive drums remain idle. However, in order to prevent the intermediate transfer belt from getting damaged by friction with the photoconductive drums, it is necessary to drive the photoconductive drums for the color image even when these photoconductive drums are not actually used to form the image. As a result, the lifespan of the photoconductive drums is shortened. A similar problem arises with a conveyance belt that transports a recording medium onto which a toner image is directly transferred from the photoconductive drums.
To address such a difficulty, there are known image forming apparatuses that employ a belt unit including an eccentric cam to enable the belt to contact and separate from the photoconductive drums.
However, such belt units are relatively large and expensive, thus hindering efforts to provide the low-cost, compact image forming apparatuses for which there is market demand.